A conventional stroke simulator 40, as shown in FIG. 5, is provided with a piston 42 and a retainer 44a that move as a result of hydraulic fluid pressure that accords with an operation force of a brake pedal; a stopper 45 that regulates a maximum movement range of the retainer 44a when increase in hydraulic fluid pressure occurs; and a first spring 46 and a second spring 47 that urge the piston 42 and the retainer 44a in a direction that resists hydraulic fluid pressure. The first spring 46 is disposed between the piston 42 and the retainer 44a, and the second spring 47 is disposed between the retainer 44a and the stopper 45.
Further, along with increase in hydraulic fluid pressure, the piston 42 moves to a side of the retainer 44a while compressing the first spring 46. Then, the piston 42 and the retainer 44a move in an integrated manner to a side of the stopper 45, while compressing the second spring 47. Due to spring reaction force at this time, a predetermined brake operation feeling is imparted to the driver.
Moreover, a shock absorbing elastic body 90a made of rubber is attached to the retainer 44a. Just before the first spring 46 is fully compressed, and just before the second spring 47 is fully compressed, the shock absorbing elastic body 90a is compressed so as to smoothly change the overall spring characteristic like a second order curve. Accordingly, a desirably brake operation feeling is imparted to the driver (for an example of the above described art, refer to Japanese Patent Laid-Open Publication No 2002-293229)
However, the fundamental simulator characteristic, namely, the relationship of the operation force of the brake pedal (hereinafter referred to as a “pedal operation force”) and a stroke of the brake pedal (hereinafter referred to as a “pedal stroke”), is determined by respective spring constants of the first spring 46 and the second spring 47, and a first stroke S1 and a second stroke S2 shown in FIG. 5. It should be noted that, the first stroke S1 corresponds to a distance in a movement direction between the piston 42 and the retainer 44a when hydraulic fluid pressure is zero, and the second stroke S2 corresponds to a distance in the movement direction between the retainer 44a and the stopper 45 when hydraulic fluid pressure is zero.
Note that, the required simulator characteristic varies between vehicle types. In order to obtained the required characteristic, there are occasions when the first stroke S1, the second stroke S2, and the overall stroke (which corresponds to S1+S2) are changed.
With the above described conventional stroke simulator 40, when the first stroke S1 is changed, it is necessary to make dimensional changes to the piston 42 or the retainer 44a. In the case that the second stroke S2 is changed, it is necessary to make dimensional changes to the retainer 44a or the stopper 45.
In the case that the overall stroke remains the same, it is possible to address the required characteristic by just making dimensional changes to the retainer 44a. Moreover, if a thickness of a base portion of the retainer 44a can be set as chosen, it is possible to simultaneously change both the strokes S1 and S2 by simply changing the thickness of the base portion of the retainer 44a. However, the retainer 44a, which has a cup-like shape, is typically made by press forming. Thus, substantial change of the thickness of the base portion of the retainer 44a is impossible. Accordingly, in the case that both of the strokes S1 and S2, and the overall stroke, are changed, it is necessary to make dimensional changes to two members.
It should be noted that, as described previously, the rubber shock absorbing elastic body 90a is provided so as to smoothly change the overall spring characteristics like a second order curve. Fundamentally, the shock absorbing elastic body 90a does not have any impact upon setting of the strokes S1 and S2.